I just sprung for 2 more monitors when I got my shiny new 7970. Its awesome. BF3 runs amazingly well across all 3 as does everything else.
My only complaint is that when I have multiple windows spread out across the displays, the bars for them are all grouped on the left by the start menu. I would love to have each window/program be in the task bar underneath its respective display.
I attached a screenshot for the visual people in the crowd to show exactly what I would like to do. I think the simplest option would be to add a hydra-grid like divider at the break in each monitor. I know that a program like display fusion is used for spreading the task bar across multiple displays, but eyefinity makes it "one" display, so I'm not sure how it would change the results. I would also not want to pay for that feature (its not in the free version) only to have to deal with trying to return it if it doesn't work.
I also know that the windows+p key allows me to switch from eyefinity to regular, but I would prefer to not have to do that.